The present invention relates to a flexible pipeline intended to connect, for example, a subsea oil well head to a subsea or floating oil production facility.
A subsea oil well head is usually connected to a subsea or floating oil production facility via several pipelines, including:
a production line consisting of a flexible pipe intended for conveying the liquid hydrocarbons; PA1 a service line consisting of one or more flexible pipes, which is intended for conveying gaseous hydrocarbons, on degassing, or compressed gas for forcing up liquid hydrocarbons; PA1 a control umbilical comprising one or more compression-sensitive hydraulic pipes and/or electrical and/or optical cables for power and/or information transmission. PA1 withstand the very high tensile loads in the case of laying at great depth; PA1 withstand the compressive loads generated by contact with a curved support or when they pass between the pads of a caterpillar-track laying or handling device; and PA1 have sufficient flexibility to withstand the combined flexural and tensile mechanical stresses due to swell. PA1 0.03d.ltoreq.j.ltoreq.0.2d, PA1 0.1d.ltoreq.j.ltoreq.0.15d,
The flexible pipes used for serving production and service lines have a high mechanical strength, in particular a high resistance to internal pressure, a high tensile strength and a high compressive resistance, and are usually laid by means of tensioning devices comprising caterpillar tracks provided with pads which grip the pipe and move translationally over a given path in order to jointly entrain it.
The tensile loads applied by these caterpillar-track tensioning devices to a flexible pipe may be considerable when laying at great depth, and the compressive forces exerted by the pads on the pipe must be high enough to avoid any relative slippage between the pads and the pipe.
The control umbilicals have a lower resistance to compressive loads than the flexible pipes serving as production or service lines, because of the presence of compression-sensitive pipes, and they cannot be laid by means of caterpillar-track tensioning devices.
The umbilicals are generally laid using winches, the tensile loads being transferred by at least one metal armouring layer located in the pipe's outer jacket.
Moreover, the electrical and/or optical cables present in the umbilicals have a low tensile strength.
Now, the tensile stresses to which the various layers of a cable bundle under bending may be subjected increase as one goes further away from the central axis (or neutral fiber).
It is therefore preferred to place the electrical and/or optical cables of a control umbilical as close as possible to the central axis. If the control umbilical has a central pipe, the latter cannot exceed a certain diameter in order to avoid subjecting the electrical and/or optical cables wound around the latter to excessively high stresses liable to break them.
In practice, the external diameter of umbilicals therefore does not exceed 200 mm.
The current trend is to increase the number of subsea well heads connected to a single production facility.
The Applicant proposed, at the Offshore Technology Conference in Houston, Tex., in 1987, simplifying the operations of laying and handling the production and service lines and control umbilicals by combining them into multipipe pipelines which are more compact and easier to handle and lay.
However, these multipipe pipelines must:
The pipelines as described in the aforementioned conference, which comprise compression-sensitive peripheral pipes, are incapable of withstanding the passage through caterpillar-track tensioning devices.
DE-A-1 918 575 relates to a multi-tube flexible pipe, but not comprising a flexible compressive-load-transferring member arranged in an annular space provided in said multiple-tube flexible pipe.
The subjet of the present invention is a novel multipipe flexible pipeline making it possible to simplify the laying and handling operations, of the type comprising a central flexible element with a high tensile strength and a high compressive strength and a plurality of peripheral pipes wound around the said central flexible element in at least one ply in an annular space lying between the said central flexible element and a jacket, at least one of the said peripheral pipes being a compression- and/or tension-sensitive pipe.
The central flexible element is typically a flexible tubular pipe of the type used for serving production lines and is manufactured in long lengths by the Applicant.
As a variant, the central flexible element comprises an assembly of several flexible tubular pipes or consists of a cable.
According to the invention, the multipipe pipeline comprises at least one flexible compressive-load-transferring member adjacent to the said at least one compression- and/or tension-sensitive peripheral pipe and arranged in the annular space lying between the said central flexible element and the said jacket.
The invention makes it possible to reconcile in a single multipipe pipeline, on the one hand, a production and/or service line and/or a cable and, on the other hand, a control umbilical.
This pipeline can be installed by means of a laying device of the type normally used for laying high-strength flexible pipes such as those serving as production or service lines, in particular a caterpillar-track tensioning device.
According to one particularly advantageous characteristic of the invention, the multipipe pipeline furthermore includes sliding means capable of allowing the said compression- and/or tension-sensitive pipe and the adjacent flexible compressive-load-transferring member to undergo relative axial movement.
The term "pipe" means here, in a general manner, both a liquid or gas pipe and a power or optical cable.
In practice, it is the power or optical cables which have the lowest tensile strength and the tensile-strength problem is consequently the most critical for these, it being possible for an excessive tensile force to break a cable.
In one embodiment of the invention, the said sliding means include a gap left between the said at least one compression- and/or tension-sensitive peripheral pipe and the said adjacent flexible compressive-load-transferring member.
Preferably, this gap j satisfies the relationship:
and preferably the relationship:
where d denotes the external diameter of the compression- and/or tension-sensitive peripheral pipe.
In one embodiment of the invention, the pipeline satisfies the relationship 2E.gtoreq.c.gtoreq.0.6E and preferably the relationship 1.6E.gtoreq.c.gtoreq.0.8E, where c denotes the width of the said compressive-load-transferring member, measured at mid-thickness of the said annular space and E denotes the thickness of the said annular space.
In one embodiment of the invention, the pipeline comprises at least two adjacent compression- and/or tension-sensitive peripheral pipes and it includes a compressive-load-transferring member between the said two adjacent peripheral pipes, the width c of which satisfies the relationship c.gtoreq.0.6E and preferably the relationship c.gtoreq.0.8E, where E denotes the thickness of the said annular space, the width c being measured at mid-thickness of the annular space.